The Multiple-Input Multiple-Output (MIMO) technology is one of the important physical layer technologies for the Long Term Evolution-Advanced (LTE-Advanced) system, and it is used to provide the space diversity gain, the spatial multiplexing gain and the array gain.
In LTE version 11 and the previous technologies, the MIMO technology uses a horizontally arranged one-dimensional (1D) linear array and has the adaptive ability in a horizontal plane, i.e., it is a two-dimensional (2D) MIMO technology. FIGS. 1-2 are schematic diagrams of structures of two conventional planar arrays. FIG. 1 is a schematic diagram of a structure of a cross-polarization two-dimensional planar array, and FIG. 2 is a schematic diagram of a structure of a uniform linear two-dimensional planar array.
In the studies of version 12, the two-dimensional planar array is introduced in combination with the technology related to the Active Antenna System (AAS), thus an adaptive control can be given in either the horizontal dimension or elevation dimension to better improve the system performance, i.e., it is a three-dimensional (3D) MIMO technology.
As illustrated in FIG. 1, each column is arranged with M cross-polarization antenna pairs in the vertical direction, and totally N columns of cross-polarization antenna pairs are arranged in the horizontal direction. As illustrated in FIG. 2, each column is arranged with M antenna arrays of the same polarization direction (the vertical polarization antennas as illustrated in FIG. 2) in the vertical direction, and totally N columns are arranged in the horizontal direction. In the above two configurations, the number of antenna ports in the horizontal direction may be equal to the number of antenna ports of the previous LTE version, such as 1, 2, 4 or 8, etc. A plurality of physical antennas in the vertical direction may form a virtual physical antenna port to reduce the number of antenna ports which transmit reference signals. When there is one antenna port in the vertical direction, the two-dimensional planar array will degenerate to the conventional one-dimensional array, while the three-dimensional MIMO technology will also correspondingly degenerate to the two-dimensional MIMO technology.
It shall be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it shall not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.